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How to Plant Onions at Home: Basic Growing Guide

If you’re planning on adding onions to your vegetable garden next growing season, that’s a good idea. They are easy to grow and can be planted from seeds, sets, or seedlings.

Onions take 100 to 175 days to reach the harvesting stage, depending on the variety and growing conditions. However, the best time to plant them is in spring or fall.

Below is a basic guide on how to grow onions. 

How to Grow Onions From Seed

Start the seeds indoors in a container with rich compost or potting soil. However, it’s best to start them 8–10 weeks before you plan to transplant them in the garden.

You can also soak the seeds first for better germination. Also, follow the packaging details as instructions may vary by climate and variety.

Keep the soil moist and place the container in a warm area until the seeds sprout. Once they sprout, place the container in a cool area where it gets ample light. Finally, transplant when the seedlings are mature enough.

Planting Onion Sets 

Onion sets are miniature bulbs that, once put into the soil, will develop into full-size bulbs after 3 to 4 months.

These are a bit more robust and grow much faster than seeds. Plant approximately 4 inches apart in rows 12-18 inches apart.

Also, do not bury them more than an inch deep into the soil. For best results, soak the sets in compost tea for 15 minutes before planting.

Additionally, when picking up bulbs at a nursery, you should check that they are dry (typically bought in mesh bags) and firm. Checking for leaf and bulb health before planting is essential for the eventual output of the mature plant (5 to 6 inches tall). 

Spacing 

Spacing will be dependent on planting from seeds or sets.

If going for seeds, start them at least 8 weeks before ground planting, in containers, and then space approximately 4 to 5 inches apart when transplanting Closer spacing will produce smaller bulbs.

When doing sets, plant them about three inches apart. Also, add straw mulch between sets, and in between the rows.

Allow for 12 to 18 inches of spacing between rows. 

How Deep to Plant? 

First, it is crucial to amend the soil with compost and other organic fertilizers to support the onion’s growth.

Sink seeds ¼ inch deep into the soil. If planting from sets, place them approximately one inch down into the soil where they can take root.

Remember, the type of onion will also determine how deep you’ll put it in the ground. It is crucial to know your climate and variety to fully understand its growing needs. 

Watering 

For onion plants to produce high yields, they need adequate water. Therefore, provide about an inch of water per week.

Also, it is best to utilize mulch around the plants as it ensures proper saturation without making the earth too soggy.

Fertilizer Requirements

Onions require rich, fertile soil that is well-drained in which to flourish.

They also require an adequate amount of nitrogen for proper growth and development [1]. Therefore, apply a nitrogen-based fertilizer three weeks before planting, and then again three weeks after.

Phosphorus and potassium are nutrients they’ll also need, especially in the early stage. Additionally, spread some compost among the plants and rake it into the soil.

Growing From Scraps 

It is also possible to grow onions from onions. In fact, it is one of the easier vegetables to grow from scraps [2].

  • Cut off the root end and use toothpicks or other materials that can hold the scrap in place over a cup or bowl.
  • Next, fill the dish, jar, or container with water and suspend just the root end in the water.
  • Soon you’ll start to see tiny sprouts coming out the top and root-like tentacles from the bottom.
  • Afterward, place the sprouted scrap into the ground or a pot, covering until just the sprouts are above the soil line.
  • Finally, water, fertilize, and cultivate as you would with an onion that is grown from seed or set.

Another source says, to regrow onions from scrap, just cut off the root end and plant directly in moist soil in a sunny location. Try both methods to see what works best for you.

Growing in Containers 

You can grow onions in shallow containers of at least eight inches deep, either from sets or seeds.

  • Fill the container about halfway with soil, and keep it watered but well-drained once planted.
  • Add rich compost until the bulbs appear.
  • The bulb should remain at least an inch under the soil, and if exposed, cover them up.
  • Additionally, cut back the leaves to help the plant focus more fully on the development of the bulbs.

Onion Companion Plants 

Anything in the cabbage family makes a great companion plant for onions.

Onions help to deter aphids, Japanese beetles, carrot flies, and rabbits, so any crop that these pests enjoy can be planted together with onions.

Additionally, lettuce and carrots, for instance, have very different root systems that won’t compete for the same resources under the soil. Moreover, tomatoes, lettuce, and strawberries are other great companion plants.

Strawberries, for instance, benefit from being close to onions, which help deter diseases that affect the strawberry plant. However, avoid all varieties of peas and beans as they do not grow well near onions.

Harvesting

How do you know when onions are ready? Firstly, the top green leaves that start to wilt are an indication that they are near harvesting. The bulbs will continue into maturity as the leaves start to lose their color.

This occurrence is due to the plant now putting all reserves toward the aging of the bulb itself. If any have flowers on the stalks, they should be harvested immediately.   

When harvesting, pull on the tops to safely remove the whole plant from the soil. Next, shake the dirt off from around the bulbs.

Finally, let the bulbs sit in the garden for 1-2 days to allow natural drying. Curing by allowing them to dry will be evident as their outer layers tighten around the bulb and dry. 

Pest and Diseases  

  • Onion fly is one of the most prolific pests that affect the entire allium family. They lay eggs and hatch maggots that feed upon the seedlings. This fly resembles the house fly. After 3 days of egg-laying, they mature and burrow their way into the onion.
  • The lesser bulb fly looks similar but is smaller. Once infected by them, the plants must be dug up and destroyed.
  • Thrips are another insect that lays eggs on the leaves and then sucks the plant sap.

There may also be many diseases due to uncontrolled watering, resulting in lesions and rot signature on the plant.

Diseases include neck rot, purple blotch, damping off, downy mildew, and green mold. 

Storing 

Store onions in dry and cool locations. If too moist or warm, resprouting can occur.

Mesh bags, bushel baskets, or cardboard boxes with holes provide the best storage to keep them dry and cool for the short term.

However, keep in mind that onions will only last about seven to ten days before thoroughly drying out or resprouting even in the best conditions.

This is true in most mild varieties but may be extended weeks or even months in proper conditions for pungent types.

See also: How to Plant Garlic: A Basic Growing Guide

Takeaway

Planting onions in your garden is a rewarding venture. Whether you will start with seeds or sets, various factors will help determine the length of growth. Additionally, you will need cool storage and dry conditions to properly enjoy your harvest.

Sasha Brown

Blogger and lover of all things natural.

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